PvAMT1;1, a Highly Selective Ammonium Transporter That Functions as H+/NH4+ Symporter

被引:59
作者
Ortiz-Ramirez, Carlos [1 ]
Mora, Silvia I. [1 ]
Trejo, Jorge [1 ]
Pantoja, Omar [1 ]
机构
[1] Univ Nacl Autonoma Mexico, Inst Biotecnol, Dept Biol Mol Plantas, Cuernavaca 62250, Morelos, Mexico
关键词
CRYSTAL-STRUCTURE; ESCHERICHIA-COLI; PLASMA-MEMBRANE; ION-TRANSPORT; RICE ROOTS; NH4+; PROTEINS; AMTB; ARABIDOPSIS; MECHANISMS;
D O I
10.1074/jbc.M111.261693
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
One of the main forms of nitrogen assimilated by microorganisms and plants is ammonium, despite its toxicity at low millimolar concentrations. Ammonium absorption has been demonstrated to be carried out by highly selective plasma membrane-located transporters of the AMT/MEP/Rh family and characterized by the presence of a well conserved hydrophobic pore through which ammonia is proposed to move. However, uncertainties exist regarding the exact chemical species transported by these membrane proteins, which can be in the form of either hydrophobic ammonia or charged ammonium. Here, we present the characterization of PvAMT1;1 from the common bean and demonstrate that it mediates the high affinity (micromolar), rapidly saturating (1 mM) electrogenic transport of ammonium. Activity of the transporter is enhanced by low extracellular pH, and associated with this acidic pH stimulation are changes in the reversal potential and cytoplasm acidification, indicating that PvAMT1; 1 functions as an H+/NH4+ symporter. Mutation analysis of a unique histidine present in PvAMT1; 1 (H125R) leads to the stimulation of ammonium transport by decreasing the K-m value by half and by increasing the V-max 3-fold, without affecting the pH dependence of the symporter. In contrast, mutation of the first conserved histidine within the channel modifies the properties of PvAMT1; 1, increasing its K-m and V-max values and transforming it into a pH-independent mechanism.
引用
收藏
页码:31113 / 31122
页数:10
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